Removing hardware isolation in general is not a good idea. There are enough hardware errors to cause problems. You don't want a bitflip to cause everything on your server to become corrupted. (Bitflips can be reduced by using ECC ram. But still, the principle remains.) (Worse: you don't want someone to be able to take over your entire physical server from one of the virtual servers)

One option would be for the kernel to temporarily mark the page(s) referenced as read-only, and do copy-on-write where necessary. This would prevent the (presumably) common case of not having the page modified by another thread while the kernel processes the data to not incur the delay of copying the data. Might only be worth it for larger amounts of data, though.